Updates are generally meant to improve the experience of a piece of software or a product. Sometimes they add new features, fix bugs, and whatnot, but when an update causes undesirable effects, that’s kind of a bummer. Unfortunately this is something that Google is dealing with at the moment with Android Wear 5.1.1.
There have been multiple reports in the past about how Android Wear 5.1.1 is excessively draining the battery of the devices it is installed on. This was first noticed on the Sony SmartWatch 3, but later more users of Android Wear devices started to complain about the problem as well.
The good news is that Google has since acknowledged the issue on the Google Product Forums, promising that they are working on resolving the issue and will be issuing a patch to fix it at the earliest. but unfortunately until we get an actual date from Google, it’s pretty much anyone’s guess as to when that might be.
In the meantime there are users who have had some success by rebooting their devices after which the battery drain appeared to be less severe, but it is not a permanent fix and it’s one that Google definitely needs to address ASAP, given how much flack smartwatches are getting these days with regards to battery life.